This invention relates to a ventilation system for use with devices which produce airborne impurities, such as cooking grills, deep fat fryers and the like. More particularly, the invention relates to such a system which includes a hood which is to be disposed over a device which produces airborne impurities and is operatively associated with blowers for respectively supplying untempered air to space beneath the hood and for exhausting air, airborne impurities and possibly flue gas from the space beneath the hood.
For many years, various systems have been provided for exhausting air and airborne impurities, including flue gas if present, from the upper surfaces of cooking grills, deep fat fryers and the like. These known, conventional exhaust systems have two distinct shortcomings. Firstly, these early exhaust systems had low energy efficiencies because the tempered air, whether heated or air-conditioned, was constantly being removed from the premises in question and often exhausted to the outside of the building in which the premises were located. Secondly, the air being exhausted, with its airborne impurities which may and often did include grease particles and the like, remained very hot and could not be effectively captured by filters positioned in the exhaust path of the material, the fat and grease often accumulating to a hazardous degree on the walls of ducts of the exhaust system.
Ventilating systems have been proposed which utilize untempered, makeup air to remove objectionable fumes, vapors and the like emitted from a localized zone such as space above cooking ranges and the like. The untempered, makeup air is supplied to a localized zone over the cooking device or the like which reduces to a considerable degree the amount of ambient air surrounding the localized zone which would otherwise be required for exhaust. One such known system provides for an air discharge aperture rearwardly adjacent to a cooking range or the like, this single, upwardly facing aperture directing a relatively high velocity, low pressure, untempered air stream upwardly into an exhaust stack positioned above the cooking unit so as to draw airborne impurities from the localized zone. Some of the untempered, makeup air in this known system is fed beneath a support for the cooking unit, with the circulation of this makeup air extending along the front of the cooking unit into the exhaust system, which can include a filter or filters for capturing condensed grease vapors and the like from the air passing therethrough. An example of this known type of ventilation system is disclosed in U.S. Pat. No. 3,400,649 entitled "Ventilating System Including Fume Removal Means" and issued to Donald D. Jensen on Sept. 10, 1968. The energy efficiency of the exhaust system was improved to a considerable degree, nevertheless distinct disadvantages still were present. Grease and fat particles carried by the air being exhausted were often insufficiently cooled to be captured by the filter, with the result that the grease or fat often built up on the interior of ducts associated with the exhaust system. Furthermore, no effective means were provided for exhausting flue gas which, if present, would serve to detract from the cooling effect of the makeup air upon the airborne materials, such as grease.
Ventilating and exhaust systems are known which include a hood in operative association with a first plenum which includes upwardly facing apertures which extend along a surface adjacent to a rear edge of a cooking surface for supplying untempered, makeup air to space between the cooking surface and a hood along the back inner wall of the hood with the air exiting these apertures carrying air with its entrained impurities such as grease, upwardly to a filter positioned within the hood. A second plenum is operatively arranged along a front edge of the hood, a plurality of louvers or a slot being provided for directing untempered, makeup air from the front plenum into the upper portion of the space beneath the hood. Exhaust and ventilating systems of this known type have been disclosed, for example, in U.S. Pat. No. 4,043,319 entitled "Exhaust Hood" and issued to Donald D. Jensen on Aug. 23, 1977 and in U.S. Pat. No. 4,089,327 entitled "Kitchen Exhaust System" and issued to Clarke T. Welsh on May 16, 1978. It is believed that the ratio of untempered, makeup air to ambient air around the cooking unit which is exhausted is improved by these known systems. Nevertheless, systems of this known type have no provision for intensively cooling the air with its entrained impurities, such as grease, rising from the cooking surface especially near the back edge of the cooking surface. No provisions are made to reduce the heating effect of flue gas. Moreover, all of the air with airborne impurities must be exhausted from beneath the hood through the filter or filters provided between an exhaust plenum and the space beneath the hood.
A ventilator for cooking units having a forwardly disposed cooking area and a rearwardly disposed, upstanding flue provided for exhausting combustion products is known. The ventilator includes a free standing floor-supported hood of box-like shape which opens forwardly and downwardly to receive a cooking unit. A hood is formed by the box like inner and outer shells so as to define a single continuous air flow space. A pair of flow directing louvers extend along forward edges of the hood so as to supply makeup to the cooking area, which makeup air picks up air with the airborne impurities, such as grease, appearing over the cooking surface of the cooking unit and under the control of an exhaust suction fan effects the passage of such air with its airborne impurities through a filter or filters into an exhaust plenum. The flue is positioned adjacent a rear wall of the hood and extends upwardly along the rear wall to a point rearward of the filter or filters. A passageway is provided between space adjacent the flue and the interior of the exhaust plenum, a damper being provided within the passageway to control the exiting of flue gas. No provision is made for cooling the flue gases, which are believed to effect a heating of the filter or filters by virtue of the uncooled flue gases being present in the exhaust plenum, a distinct disadvantage. Moreover, because of the presence of an upstanding exhaust stack for the flue gases adjacent the rear wall of the hood, untempered makeup air cannot be injected into the space between the hood and the cooking surface from the rear wall, another distinct disadvantage and shortcoming.
As illustrations of the general prior art relating to ventilation and exhaust systems which can be advantageously associated with cooking units and the like, the following U.S. patents are of general interest:
______________________________________ No. 3,260,189 D. D. Jensen July 12, 1966, No. 3,292,525 D. D. Jensen Dec. 20, 1966, No. 3,386,365 D. D. Jensen June 4, l968, No. 3,616,744 D. D. Jensen Nov. 2, 1971, No. 3,813,856 D. D. Jensen June 4, 1974 No. 4,143,645 S. Blumberg Mar. 13, 1979 and No. 4,200,087 C. T. Welsh Apr. 29, 1980. ______________________________________